The current obstetrical practice at birth in the United States is that the umbilical cord of the infant is clamped immediately. When immediate clamping occurs, 20 to 40% of the fetal-placental blood volume is left behind in the placenta. This blood contains enough iron-rich red blood cells to meet the infant's iron needs for the first 4 to 6 months of life. Delaying cord clamping has been shown to increase early iron stores without contributing to adverse outcomes. Early iron sufficiency is essential for long term neurologic health. Iron deficiency in infancy adversely affects cognitive, motor, socio-emotional, and behavioral development. Human and animal studies have shown that inadequate iron stores in early infancy have an irreversible negative impact on the developing brain with deficits persisting even after iron levels have been restored by iron supplementation. Iron is an essential component of myelination which is critical for normal brain development and function. Myelination, which peaks during the first year of life, establishes and maintains efficient communication between the discrete regions of the brain. Abnormal myelination underlies a variety of childhood developmental disorders including conditions such as autism. The gap is that the effect of increased iron stores from delayed cord clamping on myelination and neurodevelopment during early childhood is unknown. Our hypothesis is that placental transfusion affects myelination and early childhood development in the following ways: 1) placental transfusions lead to increased blood volume (BV) and red cell volume (RCV) at birth; 2) increased RCV results in more available iron for early body iron stores; 3) increased body iron stores provide essential iron supply for optimal myelination; 4) optimal myelination results i improved developmental and cognitive performance. We propose a randomized controlled longitudinal (birth to 24 months) trial of 128 infants to measure the effect of placental transfusin on the structure and function of the developing brain. We will use a non-invasive neuroimaging technique to measure myelin acquisition over time and to correlate the findings with iron stores and developmental outcomes. Enrolled women will be randomized at birth to the immediate cord clamping group or the delayed cord clamping group. We will assess infants for iron sufficiency and myelin deposition at 4 and 10 months and evaluate developmental outcomes at 4, 10, and 24 months. This study will help to establish a scientific basis for the timing of cord clamping with reference to brain development. The innovation of this study is in the simplicity of delaying cord clamping combined with the use of a new method of MRI that can quantify myelin deposition. This low-tech change in a clinical practice has the potential to reduce iron deficiency and improve developmental outcomes. If delayed cord clamping demonstrates protective effects for optimal development, changing practice will translate into a large cost savings improving lifetime productivity beneficial to society as a whole.